El Poli-Tereftalato de Etileno y caucho en desuso, se encuentran toneles en los vertederos, en los ríos y océanos, su tasa de degradación es lenta, en la actualidad se han convertido parte de la crisis ecológica. Es vital un cambio de paradigma para tener un desarrollo sostenible. Se plantea reutilizar estos recursos para contribuir a construir sustentable, sostenible y ecológico. Este estudio tiene como objetivo, demostrar que la propuesta diseño de concreto con sustitución parcial de los agregados por PET y caucho reciclados mejorará sus propiedades mecánicas, en veredas, incrementando su vida útil, su resistencia a la meteorización, la acción química y el desgaste. Se empleó metodología con nivel de investigación exploratoria y diseño de investigación experimental. Se analizó los resultados de los 84 ensayos, todas las muestras superaron al concreto convencional, siendo la muestra tres con mejores valores, supero resistencia a compresión en 8.38%, resistencia a la flexión en 19.17%, resistencia a la tracción en 24.16% y disminución de densidad 13.17%. Se concluye que, se logra el objetivo de esta investigación, tales como la disminución de la densidad del concreto, aumenta la resistencia a la compresión, tracción y flexión, ello represente ventajas medio ambientales y sociales. Sin embargo, la desventaja es que representa mayores costos en 47.01% respecto a la muestra patrón. / Disused Polyethylene Terephthalate and rubber, barrels are found in landfills, in rivers and oceans, their degradation rate is slow, now they have become part of the ecological crisis. A paradigm shift is vital for sustainable development. It is proposed to reuse these resources to contribute to building sustainable, sustainable and ecological. The objective of this study is to demonstrate that the proposed concrete design with partial replacement of aggregates by recycled PET and rubber will improve its mechanical properties in sidewalks, increasing its useful life, resistance to weathering, chemical action and wear. An exploratory research level methodology and experimental research design were used. The results of the 84 tests were analyzed, all the samples surpassed the conventional concrete, being the sample three with the best values, I surpass compression resistance in 8.38%, flexural resistance in 19.17%, tensile strength in 24.16% and decrease density 13.17%. It is concluded that, the objective of this research is achieved, such as the decrease in the density of the concrete, the resistance to compression, traction and flexión increases, this represents environmental and social advantages. However, the disadvantage is that it represents higher costs in 47.01% compared to the standard sample. / Tesis

El ángulo de fricción y la cohesión son parámetros de resistencia al corte establecidos por el modelo de Morh Coulomb, siendo estos necesarios para el diseño de estructuras geotécnicas utilizadas tanto en obras civiles como en obras mineras. Si durante la investigación geotécnica se concluye que las características de resistencia del material son menores a los requeridos, entonces es necesario realizar mejoras en terreno de fundación. Una de estas mejoras corresponde al uso de partículas PET, la misma que es mezclada con el suelo del terreno natural, obteniéndose un suelo con mejores características geotécnicas. El uso de las partículas PET como material de reforzamiento mecánico del suelo, nace de la necesidad técnica de obtener mejores características en el suelo y la búsqueda de reducir el impacto ambiental. La presente investigación busca encontrar el porcentaje óptimo de PET, que mejore el comportamiento geotécnico de un suelo gravoso arcilloso. Se preparó 5 probetas, donde se mezcló el suelo con porcentajes de 1%, 1.5%, 2%, 2.5% y 3 % de PET. Mediante el ensayo de corte directo se estimó la influencia del PET en la resistencia al corte del suelo. Los resultados obtenidos demuestran que el 2% de PET añadido a la grava arcillosa, aumenta la resistencia al corte en un 8.3% respecto al suelo sin refuerzo. / The angle of friction and cohesion are parameters of resistance to cutting that define the characteristics of the soil in civil works and buildings. If during the elaboration of a project, the soil does not comply with the necessary requirement, the way to improve or stabilize the soil to be used in the work is sought. The use of PET particles as a material for mechanical reinforcement of the soil, arises from the technical need to obtain better characteristics in the soil and the search to reduce the environmental impact. The present research seeks to find the optimal percentage of PET, which improves the geotechnical behavior of a clayey soil. Five test pieces were prepared, where the soil was mixed with percentages of 1%, 1.5%, 2%, 2.5% and 3% of PET. Through the direct cut test you will find the variation of the cut resistance generated by adding PET particles. The results obtained will be analyzed to understand the influence of the addition of recycled PET waste on the cut resistance of a clayey soil. / Tesis

Thermomonospora curvata is a thermophilic actinomycete hylogenetically related to Thermobifida fusca that produces extracellular hydrolases capable of degrading synthetic polyesters. Analysis of the genome of T. curvata DSM43183 revealed two genes coding for putative polyester hydrolases Tcur1278 and Tcur0390 sharing 61% sequence identity with the T. fusca enzymes. Mature proteins of Tcur1278 and Tcur0390 were cloned and expressed in Escherichia coli TOP10. Tcur1278 and Tcur0390 exhibited an optimal reaction temperature against p-nitrophenyl butyrate at 60°C and 55°C, respectively. The optimal pH for both enzymes was determined at pH 8.5. Tcur1278 retained more than 80% and Tcur0390 less than 10% of their initial activity following incubation for 60 min at 55°C. Tcur0390 showed a higher hydrolytic activity against poly(ε-caprolactone) and polyethylene terephthalate (PET) nanoparticles compared to Tcur1278 at reaction temperatures up to 50°C. At 55°C and 60°C, hydrolytic activity against PET nanoparticles was only detected with Tcur1278. In silico modeling of the polyester hydrolases and docking with a model substrate composed of two repeating units of PET revealed the typical fold of α/β serine hydrolases with an exposed catalytic triad. Molecular dynamics simulations confirmed the superior thermal stability of Tcur1278 considered as the main reason for its higher hydrolytic activity on PET.:Introduction; Materials and methods; Results; Discussion

No description available.

[pt] O presente estudo apresenta o comportamento dos solos reforçados com PET em pó e triturado, através de ensaios de laboratório. Foram utilizados três solos: um solo coluvionar, uma areia limpa e mal graduada e uma bentonita. Caracterização física, química e ensaios mecânicos (triaxiais CIU e cisalhamento direto) foram realizadas para cada material e misturas. O ensaio triaxial foi realizado em amostras de solo argiloso compactado com porcentagens de pó de PET de 0, 10, 20 e 30 por cento de PET triturado de 3,0 e 5,0 por cento, por seco peso de solo. Os ensaios triaxiais, em amostras de areia foram feitas a uma densidade relativa de 50 por cento e 10 por cento de teor de umidade, e com 0, 10 e 20 por cento de pó de PET, em relação ao peso seco do solo. Os ensaios de cisalhamento direto com bentonita foram feitos com porcentagens de 0 e 30 por cento de pó de PET e 3,0 e 5,0 por cento de PET triturado, por peso seco de solo. Os resultados mostraram que o teor de PET e nível de confinamento têm influência sobre o comportamento mecânico final das misturas. Com ambos os resíduos de PET, as misturas apresentam um comportamento satisfatório, aumentando ou mantendo os parâmetros de resistência ao cisalhamento semelhantes ao solo puro. Assim, para as misturas argilosos, a mistura com 30 por cento de pó de PET e a com 5 por cento de PET triturado são mais eficazes, uma vez que nelas observou-se maior melhora nos parâmetros de resistência. Para misturas de areia a inclusão PET é mais eficaz com 10 por cento de pó PET em tensões confinantes menores e umidade ótima de 10 por cento. Para misturas bentonita, a inserção de PET é mais eficaz para o PET triturado na porcentagem de 5 por cento. Portanto, o uso de resíduos de PET para o reforço do solo poderia minimizar os problemas atuais disposição do resíduo, contribuir com a redução do consumo de recursos naturais e dar um uso nobre para este material. / [en] This study presents the behavior of soils reinforced with crushed PET (Polyethylene Terephthalate) residue through experimental study. Three soils were used: a coluvionar soil, a clean and poorly graduated sand and a bentonite. Physical characterization, chemical and mechanical tests (isotropically consolidated-drained triaxial and direct shear) were performed for each material and mixtures. The triaxial test was performed on samples of clayey soil compacted within the maximum dry density and optimum moisture content with ratios of 0, 10, 20 and 30 per cent of fine crushed PET and 3,0 and 5,0 per cent of PET flakes, by dry weight of soil. The triaxial tests on sand samples were made to a relative density of 50 percent and 10 per cent of water content, and with 0, 10 and 20 percent fine crushed PET, by dry weight of soil. The direct shear tests with bentonite were made with ratios of 0 and 30 percent of fine crushed PET and 3,0 and 5,0 percent of PET flakes, by dry weight of soil. The results have shown that the PET content and level of confining stress have influence on the final mechanical behavior of the mixtures. With both residue of PET, the mixtures present a satisfactory behavior, increasing or maintaining the shear strength parameters similar to the pure soil. Thus, for the clayey mixtures, the fine crushed PET content of 30 percent and the PET flakes content of 5 percent are more effective, once they increase the strength parameters. For sandy mixtures the PET inclusions is more effective with 10 percent of fine crushed PET at lower confining stresses and the optimum content is 10 percent. For bentonite mixtures the PET inclusions is more effective for PET flakes and the optimum content is 5. Therefore, the use of PET waste for soil reinforcement could minimize the current problems of waste disposal, contribute with the reduction of consumption of natural resources and give a noble use for this material.

<p>Temperature is the common accelerant that is used for shelf-life determination of shelf-stable food because it is easy to use and there are models such as Q₁₀and Arrhenius, which are available for shelf-life prediction. The accelerated shelf-life test (ASLT) still requires months of analysis time as it only uses temperature as the accelerant. Oxygen pressure as an accelerant has not been given much attention even though many studies have shown the negative impact of oxygen on the shelf-life of food. An effective analysis method with multiple accelerants has the potential for the development of a rapid shelf-life determination method. Hence, this research focused on the invention of a rapid method, named the Ultra-Accelerated Shelf-Life Test (UASLT) that combines oxygen pressure and temperature as accelerants and the development of shelf-life prediction model(s). The study hypothesized that the application of elevated oxygen pressure and elevated temperature (40C) increases the amount of oxygen diffusing into packaged food which leads to rapid degradation of nutrients that further reduces the overall shelf-life analysis time compared to the ASLT method. A custom-made high-pressure chamber with a 100% oxygen environment at 40C was designed and developed as part of the UASLT method. The impact of the application of oxygen pressure on oxygen diffusivity in polymeric food packaging materials was investigated on three packages with different oxygen permeability properties. The application of oxygen pressure significantly increased the rate of oxygen transfer and the oxygen diffusivity values for all packaging materials compared to the counterparts that were not exposed to the pressure. A shelf-stable model food fortified with vitamins A, B1, C and D3 was developed to investigate the effectiveness of the UASLT method in degrading the quality indicators in the model foods in a polyethylene terephthalate (PET) container. PET was chosen as it was the most permeable to oxygen. Model food was also subjected to ASLT conditions at the same temperature without additional pressure and at room temperature (control). A degradation of 27.1 ± 1.9%, 13.9± 2.1%, 35.8 ± 1.0%, and 35.4 ± 0.7% were seen in vitamins A, B1, C and D3, respectively, in just 50 days. Slower degradation was observed with samples kept under the ASLT conditions for 105 days and reached a degradation of 24.0 ± 2.0%, 4.9 ± 6.1%, 32.0 ± 3.1% and 25.1 ± 1.5% for vitamin A, B1, C and D3, respectively. The control samples that were studied for 210 days showed 14.9 ± 5.0%, 2.0 ± 2.2%, 13.8 ± 2.2% and 10.6% ± 0.8% degradation in vitamins A, B1, C and D3, respectively. The increase in the dE values due to browning in samples kept at the UASLT, ASLT and control conditions were 11.67 ± 0.09, 7.49 ± 0.19 and 2.51 ± 0.11, respectively. The degradation of vitamins A, C, D3 was analyzed using the 1st order kinetic and the rate constant,    (day^-1) was used to develop four prediction models. Vitamin B1 values were omitted from the kinetic analysis due to insufficient degradation. Two temperature-oxygen diffusion models were developed by correlating oxygen diffusivity and   . Comparisons were made with the temperature-based models of    and Arrhenius. The predicted    values across the models were in the range of 0.051-0.054 day^-1,0.080-0.088 day^-1 and 0.048-0.051 day^-1, for vitamin A, C and D3, respectively. The    values estimated for vitamins A, C, and D3 were 2.16, 2.63 and 2.62, respectively. The predicted shelf-life of vitamin A, C and D3 to undergo 25% reduction was in the range of 404 to 551, 321-353 and 529-583 days across all models, respectively. The shelf-life predicted from the temperature-oxygen diffusion models was close to the temperature models indicating the potential to be paired with the UASLT method. Experimental verification is needed to analyze the errors in the prediction. The addition of oxygen pressure further reduced the shelf-life analysis time by 50% compared to ASLT. Elevated external oxygen pressure can be used as an accelerant along with elevated temperatures (40C) for rapid shelf-life testing of packaged foods. This novel approach has potential application in the food industry for faster shelf-life analysis of food.</p>

Polyethylene Terephthalate (PET) is one of the most important polymers in use today for packaging due to its outstanding properties. The usage of PET has grown at the highest rate compared with other plastic packaging over the last 20 years, and it is anticipated that the increase in global demand will be around 6% in the 2010 ¿ 2015 period. The rheological behaviour, thermal properties, tensile modulus, permeability properties and degradation phenomena of PET/clay nanocomposites have been investigated in this project. An overall, important finding is that incorporation of nanoclays in PET gives rise to improvements in several key process and product parameters together ¿ processability/ reduced process energy, thermal properties, barrier properties and stiffness. The PET pellets have been compounded with carefully selected nanoclays (Somasif MAE, Somasif MTE and Cloisite 25A) via twin screw extrusion to produce PET/clay nanocomposites at various weight fractions of nanoclay (1, 3, 5, 20 wt.%). The nanoclays vary in the aspect ratio of the platelets, surfactant and/or gallery spacing so different effect are to be expected. The materials were carefully prepared prior to processing in terms of sufficient drying and re-crystallisation of the amorphous pellets as well as the use of dual motor feeders for feeding the materials to the extruder. The rheological properties of PET melts have been found to be enhanced by decreasing the viscosity of the PET i.e. increasing the ¿flowability¿ of the PET melt during the injection or/and extrusion processes. The apparent shear viscosity of PETNCs is show to be significantly lower than un-filled PET at high shear rates. The viscosity exhibits shear thinning behaviour which can be explained by two mechanisms which can occur simultaneously. The first mechanism proposed is that some polymer has entangled and few oriented molecular chain at rest and when applying high shear rates, the level of entanglements is reduced and the molecular chains tend to orient with the flow direction. The other mechanism is that the nanoparticles align with the flow direction at high shear rates. At low shear rate, the magnitudes of the shear viscosity are dependent on the nanoclay concentrations and processing shear rate. Increasing nanoclay concentration leads to increases in shear viscosity. The viscosity was observed to deviate from Newtonian behaviour and exhibited shear thinning at a 3 wt.% concentration. It is possible that the formation of aggregates of clay is responsible for an increase in shear viscosity. Reducing the shear viscosity has positive benefits for downstream manufacturers by reducing power consumption. It was observed that all ii three nanoclays used in this project act as nucleation agents for crystallisation by increasing the crystallisation temperature from the melt and decreasing the crystallisation temperature from the solid and increasing the crystallisation rate, while retaining the melt temperature and glass transition temperatures without significant change. This enhancement in the thermal properties leads to a decrease in the required cycle time for manufacturing processes thus potentially reducing operational costs and increasing production output. It was observed that the nanoclay significantly enhanced the barrier properties of the PET film by up to 50% this potentially allows new PET packaging applications for longer shelf lives or high gas pressures. PET final products require high stiffness whether for carbonated soft drinks or rough handling during distribution. The PET/Somasif nanocomposites exhibit an increase in the tensile modulus of PET nanocomposite films by up to 125% which can be attributed to many reasons including the good dispersion of these clays within the PET matrix as shown by TEM images as well as the good compatibility between the PET chains and the Somasif clays. The tensile test results for the PET/clay nanocomposites micro-moulded samples shows that the injection speed is crucial factor affecting the mechanical properties of polymer injection moulded products.

Polyethylene terephthalate (PET) is an excellent material for bottling water, beverages, edible oils and other liquids because it is light, tough and transparent. PET bottles are also extensively reused for storage of drinking water, beverages and other liquids and for solar disinfection of microbiologically unsafe drinking water in the tropics. In spite of the usefulness of PET bottles earlier works have reported leaching of antimony and acetaldehyde from the bottle matrix into the liquid contents. Both antimony trioxide and acetaldehyde belongs to Group 2B (possible carcinogens) in the International Agency for Research on Cancer (IARC) carcinogen classification. Additionally acetaldehyde associated with alcoholic beverages (derived from alcoholic beverage and formed endogenously) has recently been upgraded to IARC Group 1 carcinogen (carcinogenic to humans). The research aims to assess the pattern and extent of antimony and acetaldehyde migration from British and Nigerian polyethylene terephthalate bottles into bottle contents under typical use and reuse conditions. The research compares the assessed extents of migration with the current regulations to determine whether the maximum acceptable levels of antimony and acetaldehyde are being exceeded and whether current regulations might need to be reassessed. To achieve these goals the pattern and extent of PET bottle use and reuse in Britain and Nigeria were appraised through survey. The survey revealed that new bottles with contents are typically stored prior to use for periods ranging between one and 7 days, with Nigerians storing for longer periods than British respondents. However storage of up to one year was reported. The extent of bottle reuse was high and similar for the two countries. Nevertheless Nigerian respondents reuse bottles for longer periods than British respondents. The survey findings together with relevant literature were used to design laboratory experiments that assessed the extent of antimony and acetaldehyde migration from PET bottles into water/beverages. A total of 82 brands of bottled water and soft drinks in plastic and glass bottles and in cartons were collected. A few samples from Nigeria in plastic pouches were collected. Materials used in bottling including glass and plastic bottle materials, metal and plastic bottle cap materials and plastic cap lining materials were collected. All samples were collected in supermarkets and shops in Britain and Nigeria except drinking water from taps which was collected in Britain only. Some bottles were aged for the purpose of studying the impact of bottle aging on chemical migration. Other bottles were stored with their contents to study the impact of long term storage of bottle contents on chemical migration. Energy dispersive X-ray spectrometry (EDX) and Raman spectroscopy were used to characterise PET bottle material and other materials associated with water and soft drink bottling. Antimony and other trace metals in water and soft drinks were determined using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Antimony content of PET and other plastics was determined by microwave digestion and ICP-MS. Acetaldehyde content of water and soft drinks and PET were determined using headspace gas chromatography with flame ionisation detection (GC-FID). Accuracy and precision for determination of antimony and other trace elements in bottle materials and bottle contents were good as recoveries were around 100% and coefficients of variation were less than 15% for all analysis types. Accuracy and precision for determination of acetaldehyde in bottle materials and bottle contents were also good as recoveries were around 100% and coefficients of variation were less than 15% for all analysis types. Impact of long term storage, elevated temperatures, bottle thickness, carbonation, bottle aging and bottle size on migration of antimony and acetaldehyde were also assessed. All plastic bottle materials analysed were found to be PET. Bottle cap materials were either polyethylene or polypropylene. All plastic cap lining materials from Britain and some from Nigeria were found to be ethylene vinyl acetate/polypropylene copolymer. Plastic cap lining materials from some Nigerian soft drinks were identified as polyvinyl chloride. Glass bottle materials analysed were found to be soda-lime glass. Metal bottle caps were identified as tinplate, tin-free-steel coated with chromium or aluminium coated with chromium. The antimony concentration in 32 PET bottle materials from Britain and Nigeria were similar and ranged between 177 and 310 mg/kg with an average of 250±30 mg/kg. The concentration agrees well with the industry reported concentration of between 150 and 350 mg/kg. The concentration of residual acetaldehyde in 25 fresh PET bottle materials from Britain and Nigeria ranged between 0.95 and 12.52 µg/g. The average concentration in British and Nigerian soft drinks PET materials are 4.76 and 2.17µg/g respectively. Concentration of residual acetaldehyde was higher in soft drinks and still water PET materials than in sparkling water materials. The concentration of residual acetaldehyde decreases as the bottle wall material becomes older. Also the thinner the bottle walls the lower the concentration of residual acetaldehyde. Antimony concentration in 47 freshly purchased British bottled water and soft drinks ranged between 0.03 and 6.61µg/L with only one sample going above the EU acceptable limit. Concentrations of other trace elements measured were low except titanium which was detected at part per million levels in soft drinks. Lead content of a Nigerian soft drink in glass bottle stored for 2 months was above the EU acceptable limit for lead. At realistic temperatures of 40 and 60°C antimony concentration in the water remained below the EU acceptable limit even after 48 hours of exposure but the concentration exceeded the limit for most exposures at 80°C. Concentration of antimony in some Nigerian bottled water and soft drinks was above the EU limit after 11 months of storage at room temperature. Aged bottles leach lower amount of antimony than new bottles. Similarly larger bottles leach lower amount of antimony than smaller bottles. The average acetaldehyde concentrations found in British fruit juices, carbonated soft drinks, sparkling water and still water were 5113, 1458, 22 and 8 µg/L respectively. Acetaldehyde was not detected in water bottled in glass. The concentration of acetaldehyde in five fruit juice samples in PET bottles and carton was beyond the EU specific migration limit (SML) of 6mg/kg. Also the tolerable daily intake of acetaldehyde could be exceeded as a result of intake of some soft drinks and fruit juices. Acetaldehyde content in soft drinks increase with storage but the increase cannot be accounted for by the residual acetaldehyde in PET. Acetaldehyde was found to be outgassing from some bottles. It was also found to be capable of migrating from soft drinks into bottle wall. Without replenishment the concentration of acetaldehyde in solution decreases with time. The use of PVC cap lining in Nigeria as found in this study is a cause for concern as PVC is associated with health risk issues. The study recommends actions to ensure that antimony in fruit juices and other bottled products remain within the regulatory standard from bottling to consumption for the purpose of safeguarding the health of consumers. Glass used in bottling should be well scrutinized to ensure that it does not contain high levels of lead or other chemical substances that can cause harm to consumers through migration into contents. PET bottles can safely be used for solar water disinfection without the risk of antimony intake at concentrations above safe limits as water temperature achievable as the result of the technique doesn¿t go beyond 60°C. Also aged bottles are safer to use than new bottles because their chemical leaching was found to be lower than that of new bottles. This study recommends the reassessment of the absence of international guidelines for acetaldehyde in water and foods. The study also recommends that the amount of acetaldehyde that can be added to soft drinks as flavouring agent should be below the specific migration limit (SML) for migration of acetaldehyde from PET bottle into bottle contents. This is essential since the SML was designed to ensure that exposure to acetaldehyde, as a result of intake of bottled water and soft drinks in PET bottles, is below the tolerable daily intake (TDI) for acetaldehyde. As antimony was reported to go beyond the safe limits in some Nigerian bottled water and soft drinks after 11 months of storage this study discourages the use of bottle contents stored for a very long time. / Commonwealth Scholarship Commission in the United Kingdom

In view of the importance of charge storage in polymer electrets for electromechanical transducer applications, the aim of this work is to contribute to the understanding of the charge-retention mechanisms. Furthermore, we will try to explain how the long-term storage of charge carriers in polymeric electrets works and to identify the probable trap sites. Charge trapping and de-trapping processes were investigated in order to obtain evidence of the trap sites in polymeric electrets. The charge de-trapping behavior of two particular polymer electrets was studied by means of thermal and optical techniques. In order to obtain evidence of trapping or de-trapping, charge and dipole profiles in the thickness direction were also monitored. <br><br> In this work, the study was performed on polyethylene terephthalate (PETP) and on cyclic-olefin copolymers (COCs). PETP is a photo-electret and contains a net dipole moment that is located in the carbonyl group (C = O). The electret behavior of PETP arises from both the dipole orientation and the charge storage. In contrast to PETP, COCs are not photo-electrets and do not exhibit a net dipole moment. The electret behavior of COCs arises from the storage of charges only. <br><br> COC samples were doped with dyes in order to probe their internal electric field. COCs show shallow charge traps at 0.6 and 0.11 eV, characteristic for thermally activated processes. In addition, deep charge traps are present at 4 eV, characteristic for optically stimulated processes. <br><br> PETP films exhibit a photo-current transient with a maximum that depends on the temperature with an activation energy of 0.106 eV. The pair thermalization length (rc) calculated from this activation energy for the photo-carrier generation in PETP was estimated to be approx. 4.5 nm. The generated photo-charge carriers can recombine, interact with the trapped charge, escape through the electrodes or occupy an empty trap. <br><br> PETP possesses a small quasi-static pyroelectric coefficient (QPC): ~0.6 nC/(m²K) for unpoled samples, ~60 nC/(m²K) for poled samples and ~60 nC/(m²K) for unpoled samples under an electric bias (E ~10 V/µm). When stored charges generate an internal electric field of approx. 10 V/µm, they are able to induce a QPC comparable to that of the oriented dipoles. Moreover, we observe charge-dipole interaction. Since the raw data of the QPC-experiments on PETP samples is noisy, a numerical Fourier-filtering procedure was applied. Simulations show that the data analysis is reliable when the noise level is up to 3 times larger than the calculated pyroelectric current for the QPC. <br><br> PETP films revealed shallow traps at approx. 0.36 eV during thermally-stimulated current measurements. These energy traps are associated with molecular dipole relaxations (C = O). On the other hand, photo-activated measurements yield deep charge traps at 4.1 and 5.2 eV. The observed wavelengths belong to the transitions in PETP that are analogous to the π - π* benzene transitions. The observed charge de-trapping selectivity in the photocharge decay indicates that the charge detrapping is from a direct photon-charge interaction. Additionally, the charge de-trapping can be facilitated by photo-exciton generation and the interaction of the photo-excitons with trapped charge carriers. These results indicate that the benzene rings (C6H4) and the dipolar groups (C = O) can stabilize and share an extra charge carrier in a chemical resonance. In this way, this charge could be de-trapped in connection with the photo-transitions of the benzene ring and with the dipole relaxations. <br><br> The thermally-activated charge release shows a difference in the trap depth to its optical counterpart. This difference indicates that the trap levels depend on the de-trapping process and on the chemical nature of the trap site. That is, the processes of charge detrapping from shallow traps are related to secondary forces. The processes of charge de-trapping from deep traps are related to primary forces. Furthermore, the presence of deep trap levels causes the stability of the charge for long periods of time. / Angesichts der Bedeutung der Ladungsspeicherung in Polymerelektreten für viele Anwendungen, wie z.B. in elektromechanischen Wandler, ist es das Ziel dieser Arbeit, zum Verständnis der zugrundeliegenden Mechanismen der kurz- und langfristigen Ladungsstabilisierung beizutragen sowie mögliche Haftstellen zu identifizieren. Ladungs- und Entladungsprozesse in Elektreten geben Hinweise auf Ladungshaftstellen. Diese Prozesse wurden mit thermischen und optischen Methoden bei gleichzeitiger Messung von Ladungs- und Polarisationprofilen untersucht. Die experimentellen Untersuchungen der vorliegenden Arbeit wurden an Polyethylenterephthalat (PETP) und an Cyclischen-Olefin Copolymeren (COC) durchgeführt. <br><br> PETP ist ein Photoelektret und weist in der Carbonylgruppe (C = O) ein Dipolmoment auf. Die Elektreteigenschaften ergeben sich sowohl aus der Orientierungspolarisation als auch aus der Ladungsspeicherung. Im Gegensatz zu PETP ist COC kein Photoelektret und zeigt auch keine Orientierungspolarisation. Deshalb folgen die Elektreteigenschaften des COC ausschließlich aus der Ladungsspeicherung. Die COC-Proben wurden mit Farbstoffen dotiert, um das innere elektrische Feld zu untersuchen. Diese Systeme zeigen flache Ladungshaftstellen bei 0,6 und 0,11 eV, die durch thermisch stimulierte Prozesse entladen werden sowie tiefe Haftstellen bei 4 eV, die optisch stimuliert werden können. <br><br> PETP-Filme zeigen einen transienten Photostrom mit einem Maximalwert ( jp), der von der Temperatur mit einer Aktivierungsenergie von 0,106 eV abhängt. Der thermische Paarabstand (rc) kann für die Photoladungsgeneration in PETP auf ca. 4,5 nm abgeschätzt werden. Die Photoladungsträger können rekombinieren, mit den gespeicherten Ladungen interagieren, über die Elektroden entkommen oder eine leere Haftstelle einnehmen. <br><br> PETP zeigt einen kleinen quasi-statischen pyroelektrischen Koeffizienten (QPC) von ca. 0,6 nC/(m²K) für nicht polarisierte Proben, ca. 60 nC/(m²K) für polarisierte Proben und ca. 60 nC/(m²K) für nicht polarisierte Proben mit Vorspannung (E ~10 V/µm). Wenn die gespeicherten Ladungen ein internes elektrisches Feld von ca. 10 V/µm generieren können, sind sie in der Lage, einen QPC herbeizuführen, der vergleichbar mit dem von orientierten Dipolen ist. Es ist außerdem möglich, eine Ladungs-Dipol-Wechselwirkung zu beobachten. Da die QPM-Daten von PETP auf Grund des geringen Signals verrauscht sind, wurde ein numerisches Fourier-Filterverfahren angewandt. Simulationen zeigen, dass eine zuverlässige Datenanalyse noch bei einem Signal möglich ist, dessen Rauschen bis zu 3-mal größer ist als der berechnete pyroelektrische Strom. <br><br> Messungen der thermisch stimulierten Entladung von PETP-Filmen ergaben flache Haftstellen bei ca. 0,36 eV, welche mit der Dipolrelaxation der Carbonylgruppe (C = O) assoziiert sind. Messungen der photostimulierten Entladung ergaben tiefe Haftstellen bei 4,1 und 5,2 eV. Die beobachteten Wellenlängen entsprechen Übergängen in PETP analog den π - π* Übergängen in Benzol. Die beobachtete Selektivität bei der photostimulierten Entladung lässt auf eine direkte Wechselwirkung von Photonen und Ladungen schließen. Einen zusätzlichen Einfluß auf die Entladung hat die Erzeugung von Photo-Exzitonen und deren Wechselwirkung mit den gespeicherten Ladungsträgern. Diese Ergebnisse deuten darauf hin, dass die Phenylringe (C6H4) und die Dipolgruppen (C = O) eine zusätzliche Ladung in einer chemischen Resonanz stabilisieren und miteinander teilen können. Daher kann die gebundene Ladung auch durch einen Photoübergang im Benzolring oder durch eine Dipolrelaxation freigesetzt werden. <br><br> Die mittels thermisch stimulierter Entladung bestimmte Tiefe der Haftstellen unterscheidet sich deutlich von den mittels photostimulierter Entladung gemessenen Werten. Flachere Haftstellen werden bei der thermisch stimulierten Entladung gefunden und können sekundären Kräften zugeordnet werden. Die tieferen Haftstellen sind chemischer Natur und können primären Kräften zugeordnet werden. Letztere sind für die Langzeitstabilität der Ladung in Polymerelektreten verantwortlich.

Orientadores: Felix Guillermo Reyes Reyes, Maria Teresa de Alvarenga Freire / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-16T23:01:27Z (GMT). No. of bitstreams: 1 Dutra_CamilaBraga_D.pdf: 1974104 bytes, checksum: 7a0aae96f3654e27fb7d553ee756e522 (MD5) Previous issue date: 2010 / Doutorado / Doutor em Ciência de Alimentos